A new medical technique for heart attack patients involves the pulsatile retroperfusion of oxygenated blood into the myocardium from the coronary sinus. The procedure comprises advancing an autoinflatable catheter into the coronary sinus. During diastole, oxygenated blood is pumped through the catheter into the coronary sinus. The blood flowing through the catheter is under sufficient pressure to inflate the balloon which is also positioned in the sinus. Inflation of the balloon blocks a portion of the sinus which results in the unidirectional retroperfusion of oxygenated blood from the catheter through coronary veins into the myocardium. During systole, no blood is pumped through the catheter which, as a result, deflates the balloon and allows coronary venous blood to drain past the collasped balloon. Oxygenated blood is continuously pumped to the myocardium by this method until such time as the coronary arteries can be repaired.
For this procedure to operate efficiently, the balloon of the catheter must be inflatable and deflatable in a very short period of time. Typical inflation times are on the order of 50 milliseconds. This requires the free flow of blood into and out of the balloon chamber.
Some conventional autoinflatable catheters utilize holes in the catheter tube to form passages into the balloon chamber formed between the balloon and the catheter tube through which the blood flows for inflating and deflating the balloon. The number and size of the holes are sufficiently small to not significantly weaken the catheter tube. However, the small size of the holes may cause significant damage to the blood. This is because a portion of the blood flowing through the holes and contacting the catheter wall may be damaged by the contact. The amount of damage to the blood is related to the amount of blood contacting the catheter wall as it flows into the balloon chamber, which in turn is dependent on the size of the holes.
In addition, the small size of the holes tends to restrict the free flow of blood into and out of the balloon chamber resulting in undesirably slow inflation and deflation of the balloon. To compensate, increased pressure may be used, resulting in faster inflation of the balloon, but may further damage the blood as it passes through the holes. Furthermore, a small number of holes create regions in the balloon chamber where blood tends to stagnate and possibly clot.
There are other catheters which utilize an axial rod between two catheter tube sections as a balloon support. One end of the balloon is attached to each catheter tube section. This catheter design enables free flow of a liquid within the interior of the balloon but results in obstructions in each catheter tube section at the positions where the axial rod is attached to the catheter tube sections. These obstructions restrict the amount of the liquid flowing through the catheter tube to inflate the balloon. As such, catheters having an axial rod as a balloon support are not suitable for applications such as the retroperfusion of blood to the myocardium.